Hyperinsulinemic hypoglycemia: think of hyperinsulinism/hyperammonemia (HI/HA) syndrome caused by mutations in the GLUD1 gene

Background: Hyperinsulinism-hyperammonemia syndrome (HI/HA) is a rare autosomal dominant disorder presenting with hypoglycemia and hyperammonemia. It is caused by activating mutations in the GLUD1 gene. Case reports: Three patients from two different centers, a 14-month-old female, a 28-year-old female (mother of the first patient) from Toronto and an unrelated 2.5-year-old male from Vienna, presented with multiple episodes of seizures associated with hypoglycemia. Results: All patients had mild to moderate hypoglycemia, inappropriate insulin levels and mild hyperammonemia, thus suggesting a disorder of glutamate dehydrogenase (GDH). Molecular genetic testing of the GLUD1 gene identified heterozygous mutations in all patients (patient 1 and her mother a novel c.1526G>C mutation; patient 3 a known c.809C>G mutation). Conclusion: We present three new patients with GDH caused by heterozygous mutation in the GLUD1 gene. Mild hyperammonemia and inappropriately elevated insulin levels should suggest a GLUD1 mutation. Early onset hypoglycemia associated with seizures, and especially a good response to diazoxide treatment, should include this disorder in the differential diagnosis of hyperinsulinemic hypoglycemia.